Scientifically, someone would have to be completely devoid of the ability to produce dopamine in order to be totally devoid of self-interest. Even someone like Mother Teresa gets a shot of dopamine for doing something that makes her feel good.

It's basic animal nature to be self-interested.

Behaviors are not soley the function of neuro-transmitters. Even a person with Parkinsons, which is believed to be caused by a lack of L-dopa production, have self-interests or a survival instinct.